1. Field of the Invention
The invention relates generally to the production of man-made composite structural and building products. More particularly, the invention relates to the production of a cellulosic core component which can be utilized, for example, in an interior space or void formed by the shell or framework of a building product, e.g., composite doorskins.
2. Brief Description of Related Technology
Man-made boards, such as fiberboard, can be embossed or molded to have three-dimensional shapes and various design and structural features found in natural wood. Types of useful man-man boards are referred to by the following terms, for example: (a) fiberboards such as hardboard (e.g., low-density hardboard), soft board, and medium-density fiberboard and (b) chipboards such as particleboard, medium-density particleboard, and oriented strandboard ("OSB"). Composites of these boards are also useful. Such boards, particularly hardboard, have found widespread use in the manufacture of doorskins, which can be glued together or laminated to form a shell which supports or encloses a structure or a frame.
Commonly, doorskins (also referred to as door faces) are molded from a planar cellulosic mat to include one or more interior depressions or contours, such as one or more square or rectangular depressions which do not extend to the outer edge or periphery of the doorskin product. Doorskins often require inclined molded walls having a plurality of contours that include varied curved and planar surfaces. Where the depressions or contours are included on a doorskin product, this can serve to replicate a more expensive natural wood paneled door. For example, doors having two, three, four, five, and six panel designs are commonly produced. The exterior or visible surfaces of the fiberboard also can be embossed with a design that represents a wood grain pattern found in a natural piece of wood.
The principal processes for the manufacture of wood composites such as doorskins and other structural or building products include (a) wet felted/wet pressed or "wet" processes, (b) dry felted/dry pressed or "dry" processes, and (c) wet felted/dry pressed or "wet-dry" processes.
Generally in a wet process, cellulosic fillers or fibers (e.g., woody material which is subjected to fiberization to form wood fibers) are blended in a vessel with large amounts of water to form a slurry. The slurry preferably has sufficient water content to suspend a majority of the wood fibers and preferably has a water content of at least ninety percent by weight ("weight percent") of the wood fibers. The slurry is deposited along with a synthetic resin binder, such as a phenol-formaldehyde resin, onto a water-pervious support member, such as a fine screen or a Fourdrinier wire, where much of the water is removed to leave a wet mat of cellulosic material having, for example, a moisture content of about fifty weight percent, based on the dry weight of the fibers. The wet mat is transferred from the pervious support member to a press and consolidated under heat and pressure to form the molded wood composite.
A wet-dry forming process can also be used to produce cellulosic composites. Preferably, a wet-dry process begins by blending cellulosic or wood fiber raw material in a vessel with large amounts of water having a pH of less than seven to form a slurry. This slurry is then blended with the resin binder. As in the wet process described above, the blend is then deposited onto a water-pervious support member, where a large percentage of the water is removed, thereby leaving a wet mat of cellulosic material having a water content of about fifty weight percent, for example. This wet mat is then transferred to an evaporation zone where much of the remaining water is removed by evaporation. The dried mat preferably has a moisture content of less than about thirty weight percent. The dried mat is then transferred to a press and consolidated under heat and pressure to form the wood composite which may be, for example, a flat board, a doorskin, or any other desired shape depending on the intended use of the product.
In a dry process, the cellulosic fibers are generally conveyed in a gaseous stream or by mechanical means rather than a liquid stream. For example, the cellulosic fibers may be first coated with a thermosetting resin binder, such as a phenol-formaldehyde resin. The fibers are then randomly formed into a mat by air blowing the resin-coated fibers onto a support member. The mat may optionally be subjected to pre-press drying. The mat, typically having a moisture content of less than about thirty weight percent and preferably less than about ten weight percent, is then pressed under heat and pressure to cure the thermosetting resin and to compress the mat into an integral consolidated structure.
The fiber mats formed by the above-described methods can be pressed into a pre-selected decorative shape, typically at a thickness of about one-eighth of an inch. As stated above, in the case of a composite door product, the decorative shape generally includes one or more panels and/or other contours in the doorskin, as described above. Two doorskin pieces are typically joined together with an adhesive binder, which is placed at least at the contact points along the periphery of the door assembly formed by the doorskins. Because the doorskin pieces are contoured, an open, interior space of varying dimensions is formed by the doorskin assembly.
Doorskin pieces are often not used alone, but in conjunction with some other material(s) to add support to the final door product. The doorskin pieces often utilize wood framing at or near the perimeter of the assembled doorskin. It is known to use rails and stiles, which, when attached together, can provide additional structural support for the door. Rails can be generally described as horizontally-oriented beams which provide support for the door. Stiles, on the other hand, can be generally described as longitudinal or vertically-oriented beams which provide support for the door. In addition, a lock block is optionally utilized to provide further support for a door handle and/or a locking mechanism (e.g., a so-called "dead bolt") at the periphery of the door. The lock block is preferably secured to a stile and/or a rail.
However, although the structure of a man-made composite door product is supported with rails and stiles, often the door still will not perform as well as a natural solid wood door because the interior spaces defined by the doorskins will be substantially hollow or empty. The hollow spaces or voids cause the door to be lighter than is generally preferred. Further, it is often found that the sound insulation provided by such doors may not be satisfactory. Thus, it is often desirable to use a core material (e.g., core pieces or components) to fill these hollow spaces.
In the past, core materials made of corrugated cardboard and/or paper have been used. However, it has sometimes found that the sound insulation provided by doors using such core materials may not be satisfactory.
A suitable core material should also provide the door product with a desirable weight, for example the weight of a similarly-styled natural solid wood door. A typical, thirty-inch wide solid pine door weighs approximately forty-two pounds. Known core materials and components have the disadvantage, for example, that they often fall far short of the desired weight. In addition, some alternatives to doorskins having a core material (e.g., full thickness particleboard doors) produce a door that is too heavy and/or difficult to manufacture. In addition, a core material should provide the door with a relatively even weight distribution.
The core material should also have characteristics (e.g., size and shape) that allow placement and attachment within the interior spaces formed by the doorskin assembly. As described above, doorskins, particularly for paneled doors, are commonly molded to include one or more interior depressions (i.e., on the surface at some distance from the periphery), such as one or more square or rectangular depressions that do not extend to an outer edge of the doorskin. These surface depressions create varying depths (measured from the front face to the back face of the door) of the interior void formed by a pair of assembled doorskins. When placing a core material or component on the interior of the doorskin assembly, it is therefore necessary to compensate for the varying depth of the interior void.
Another problem with known core components is that different styles of door (e.g., two-, three-, four-, five-, and six-panel models) will have different patterns of hollow spaces or voids. Thus, a door manufacturer has generally been required to have readily available various sizes and patterns of core components for the different models of doorskins it wishes to use. This is undesirable because such a system requires (a) various different machinery (e.g., dies) to make the varying types of core materials and (b) the stocking of multiple sizes of the produced core materials. Such necessities make the manufacturing process more complicated and expensive. It would therefore be desirable to have a single core component design which could be used for multiple designs of doors.